This invention relates to dentistry, specifically to a unique instrument that will simplify the accurate attachment of models of the upper and lower dental arches on a dental articulator in the same relationship as occurred in the natural dentition.
In the construction of any rigid dental device that contacts both the upper and lower teeth, models of the patient's upper and lower dentition must be positioned on a dental articulator. It is important that they be related to each other in the same relationship as existed in the patient's mouth. Most functional orthodontic appliances, as well as several other oral devices such as the NAPA in U.S. Pat No. 33,442 to George Nov. 20, 1990, are designed to keep the lower jaw forward. Therefore, the models on the articular must be positioned with the lower model forward relative to the upper model.
The most common way of transferring the dental relationship in the mouth to the articulator is with a simple wax bite. The dentist softens a block of wax with heat and inserts it between the patient's upper and lower teeth. The dentist then guides the jaw to the desired position and tells the patient to hold it there while the wax cools and hardens. The models of the patient's upper and lower teeth then can be correctly related to each other by fitting them into the indentations in the wax. The models, with the wax between them, are then attached to the articulator. This is done in a manner that will allow the wax bite to be discarded and still allow the articulator, which simulates jaw movements, to open and close back to the wax bite position.
The relationship of the mandible to the maxilla is determined by the relative positions of the incisal edges of the lower to upper central incisor teeth. The distances between them are measured in three planes in space to determine their vertical, anteroposterior, and transverse relationships.
Three problems face the dentist when attempting to register this mandibular position using the free-hand wax bite technique described above.
1. The dentist must keep in mind where in space those three positions are for each individual patient. Those positions can only be estimates since he has no gauge or stop to let him know when the correct relationship has been reached. The most difficult of those is the anteroposterior. Most often this position is selected relative to the individual patient's ability to protrude the jaw, e.g. three-fourths the distance from the most retruded to the most protruded position of the mandible. Since this ability varies among patients, the dentist must remember where the most retruded and most protruded positions were, then use his judgment as to when the jaw has moved forward three-fourths that distance. The difficulty of this determination is compounded when simultaneously attempting to assure the accuracy of the other two positions.
2. The dentist must be able to communicate to the patient how far and in which direction to move the jaw, and when to stop moving. The verbal instructions must be given precisely and clearly, and they must be interpreted accurately and immediately or the correct positions will be over or undershot.
3. Some patients are poorly coordinated, and their muscular responses are not what they intend. For example, when closely approaching the correct position, they may involuntarily jerk the jaw, rendering the wax bite either unusable or imprecise.
In spite of its difficulties and inaccuracies, the free-hand wax bite technique described above remains the most commonly used method of transferring the jaw relationship as it exists in a patient to an articulator. The reason for this is that heretofore no one has devised an easier method that can properly position the jaw. Several jigs have been introduced to improve the bite registration technique, but all of them have serious shortcomings.
One such jig (U.S. Pat. No. 4,439,147 to Keys and Magill, Apr. 17, 1984) is a single-piece instrument which engages the lingual aspect of the lower incisors by which those teeth can be pulled forward until the instrument contacts the lingual aspect of the upper incisors, at which point the lower teeth are lined up directly under the upper teeth. This is the only relationship of lower to upper dental arches that this jig can produce. However, many oral devices should be constructed with the lower incisors more anterior than the upper incisors.
Another single-piece jig, trademark ExactoBite, attempts to give a greater selection of positions for the lower teeth. This instrument has a notch into which the upper front teeth are keyed and three notches into which the lower teeth may fit. However, with this instrument it is possible to relate the lower incisors in only the following three positions: directly under, approximately four millimeters ahead, and approximately four millimeters behind the upper incisors. Although the notches for the lower teeth on this jig are too far apart to allow precise positioning, they are too close together to allow easy selection when guiding the teeth to the desired bite.
No current method allows the dentist to accurately place and register the protruded position of the jaw, e.g. at precisely three-fourths the distance forward from the most retruded to the most protruded position of the jaw.
Most dentists would desire to use an instrument that would enable them to easily, accurately and reliably relate the lower jaw to the upper jaw in any position from the most posterior to the most anterior along the protrusive path.